Remote copy which is the data copy between the first and the second storage apparatuses is known. The types of remote copy are, for example, synchronous remote copy and asynchronous remote copy. If the first storage apparatus receives a write request from a host and if synchronous remote copy is adopted, after the data complying with the write request is transferred from the first storage apparatus to the second storage apparatus, a write completion response is transmitted to the host apparatus while, if asynchronous remote copy is adopted, even if the data complying with the write request is not transferred from the first storage apparatus to the second storage apparatus, the write completion response is transmitted to the host apparatus.
In a remote copy system to which asynchronous remote copy is adopted (hereinafter referred to as an asynchronous remote copy system), for example, the first storage apparatus, as well as a first DVOL (a logical volume in which the data is stored), comprises a first JVOL (a logical volume in which a journal (hereinafter referred to as a JNL) is stored). Similarly, the second storage apparatus comprises a second JVOL as well as a second DVOL. The first storage apparatus, if receiving a write request, stores the data complying with the write request in the first DVOL and, at the same time, stores the JNL of the data in the first JVOL. The first storage apparatus transfers the JNL in the first JVOL to the second storage apparatus, and the second storage apparatus writes the JNL from the first storage apparatus to the second JVOL. After that, the second storage apparatus writes the data which the JNL in the second JVOL comprises to the second DVOL. By this method, the data written to the first DVOL is considered to have been copied to the second DVOL.
In the Patent Literature 1, an asynchronous remote copy system in the multi-target method is disclosed. In the multi-target method, for one copy source, multiple copy destinations exist. As more specifically described, in the Patent Literature 1, for example, the items below are disclosed.                A first storage apparatus, a second storage apparatus, and a third storage apparatus exist.        The first storage apparatus is the copy source, and the second and third storage apparatuses are the copy destinations from the first storage apparatus.        A first host apparatus is connected to the first storage apparatus, a second host apparatus is connected to the second storage apparatus, and a third host apparatus is connected to the third storage apparatus.        The first storage apparatus comprises a first DVOL, a first first JVOL, and a second first JVOL.        The second storage apparatus comprises a second DVOL and a second JVOL.        The first and the second DVOLs are paired. The first DVOL is the primary DVOL and the second DVOL is the secondary DVOL.        The third storage apparatus comprises a third DVOL and a third JVOL.        The first and the third DVOLs are paired. The first DVOL is the primary DVOL and the third DVOL is the secondary DVOL.        The first host apparatus writes the data to the first DVOL.        The first storage apparatus writes the JNL of the data written to the first DVOL to both the first first JVOL and the second first JVOL. The JNLs, as well as the input/output target data of the host apparatus, include update numbers.        The JNL in the first first JVOL is copied to the second JVOL.        The second storage apparatus, among one or more JNLs in the second JVOL which are not reflected, reflects the JNL comprising the oldest update number in the second DVOL (writes the data which the JNL comprises to the second DVOL).        The JNL in the second first JVOL is copied to the third JVOL.        The third storage apparatus, among one or more JNLs in the third JVOL which are not reflected, reflects the JNL comprising the oldest update number in the third DVOL (writes the data which the JNL comprises to the third DVOL).        
Furthermore, according to the Patent Literature 1, if a failure occurs in the first storage apparatus, the second storage apparatus becomes the copy source and the third storage apparatus becomes the copy destination.